1. Field of the Invention
The present invention relates to a power converter including a plurality of semiconductor element rows each having a plurality of semiconductor elements connected to one another in series. The semiconductor element rows are connected to one another in parallel and at least one of the semiconductor elements in each semiconductor element row is a switching semiconductor element. More particularly, the present invention relates to an improvement of the switching semiconductor element.
2. Discussion of the Background
In recent years, semiconductor power modules in each of which a main circuit including switching semiconductor elements and a drive control circuit for controlling drive of the switching semiconductor elements of the main circuit are stored in a package as a power converter have been frequently used as a drive unit for controlling drive of an induction motor, a DC brushless motor, a switched reluctance (SR) motor, etc.
FIG. 11 is a circuit block diagram of an inverter for driving, as a background power converter, an induction motor which is a three-phase AC load. In FIG. 11, each of the reference numerals xe2x80x9c1Uxe2x80x9d, xe2x80x9c1Vxe2x80x9d and xe2x80x9c1Wxe2x80x9d denotes an insulated-gate bipolar transistor (hereinafter, referred to as an xe2x80x9cIGBTxe2x80x9d) acting as a high-side switching semiconductor element in a semiconductor element row formed by a pair of switching semiconductor elements connected to each other in series. Further, each of the reference numerals xe2x80x9c2Uxe2x80x9d, xe2x80x9c2Vxe2x80x9d and xe2x80x9c2Wxe2x80x9d denotes an IGBT acting as a low-side switching semiconductor element connected to each of the IGBTs 1U, 1V and 1W in series. Reference numerals xe2x80x9c3Uxe2x80x9d, xe2x80x9c3Vxe2x80x9d and xe2x80x9c3Wxe2x80x9d denote flywheel diodes, which are respectively connected to the IGBTs 1U, 1V and 1W in parallel, while reference numerals xe2x80x9c4Uxe2x80x9d, xe2x80x9c4Vxe2x80x9d and xe2x80x9c4Wxe2x80x9d denote flywheel diodes, which are respectively connected to the IGBTs 2U, 2V and 2W in parallel.
A U-phase semiconductor element row is formed by the IGBTs 1U and 2U and the flywheel diodes 3U and 4U and a V-phase semiconductor element row is formed by the IGBTs 1V and 2V and the flywheel diodes 3V and 4V. Meanwhile, a W-phase semiconductor element row is formed by the IGBTs 1W and 2W and the flywheel diodes 3W and 4W. In addition, connecting opposite end portions of these semiconductor element rows to one another, respectively, an inverter bridge is formed in which the U-phase, V-phase and W-phase semiconductor element rows are connected to one another in parallel.
Meanwhile, a main circuit 5 is formed in which in the U-phase, V-phase and W-phase semiconductor element rows connected to one another in parallel, a junction of collectors C of the IGBTs 1U, 1V and 1W is set as a high-potential input terminal P and a junction of emitters E of the IGBTs 2U, 2V and 2W is set as a low-potential input terminal N such that a series junction of the IGBTs 1U and 2U, a series junction of the IGBTs 1V and 2V and a series junction of the IGBTs 1W and 2W are respectively set as output terminals U, V and W.
Further, a DC main power source 6 is connected in parallel to a smoothing capacitor 7 such that a positive pole and a negative pole of the DC main power source 6 are respectively connected to the input terminal P and the input terminal N. A three-phase induction motor 8 acting as a load of the main circuit 5 is also connected to the output terminals U, V and W. Meanwhile, each of characters xe2x80x9cLuxe2x80x9d, xe2x80x9cLvxe2x80x9d and xe2x80x9cLwxe2x80x9d denotes a parasitic inductance in a line connecting an emitter E of each of the IGBTs 2U, 2V and 2W and the input terminal N.
A DC control power source 9 supplies electric power to input circuit sections of drive control circuits 10U, 10V and 10W provided for the IGBTs 2U, 2V and 2W, respectively. An amplifier 11 forms the input circuit section of the drive control circuit 10U so as to amplify and output a control signal input from an input terminal INu. A photocoupler 12 is formed by a light emitting diode LED and a phototransistor PT. An input signal output from the amplifier 11 is input to the light emitting diode LED via a protective resistance 13 and is output through its insulation, as an insulation signal, from the phototransistor PT. Namely, the photocoupler 12 employs a collector C of the phototransistor PT, which is connected to a load resistance 14, as an output terminal for the insulation signal.
Further, a drive circuit 15 forms an output circuit section of the drive control circuit 10U and receives and amplifies the insulation signal output from the photocoupler 12 so as to output a drive voltage signal to a gate G of the IGBT 2U via a gate resistance 16. A DC drive power source 17U for supplying electric power to the output circuit section of the drive control circuit 10U supplies electric power not only to the phototransistor PT by way of the load resistance 14, but also to the drive circuit 15.
As described above, the drive control circuit 10U for controlling a drive of the IGBT 2U in response to an input of the control signal from the input terminal INu is formed by the amplifier 11, the photocoupler 12, the protective resistance 13, the load resistance 14, the drive circuit 15 and the load resistance 16. In addition, the drive control circuit 10V for controlling a drive of the IGBT 2V in response to an input of a control signal from an input terminal Inv, and the drive control circuit 10W for controlling a drive of the IGBT 2W in response to an input of a control signal from an input terminal INw each have a similar arrangement. The single DC control power source 9 is provided in common as a drive power source of the input circuit sections of the drive control circuits 10U, 10V and 10W. However, the DC drive power sources 17U, 17V and 17W are respectively inserted into the output circuit sections of the drive control circuits 10U, 10V and 10W as their drive power sources.
The operation of the background inverter shown in FIG. 11 will now be described. Initially, a pulse width modulation (PWM) control circuit (not shown) is provided for outputting PWM signals for performing a variable speed control of the three-phase induction motor 8 acting as the load. Further, the PWM signals (i.e., the control signals of the PWM control circuit) are respectively input to the input terminals INu, INv and INw of the drive control circuits 10U, 10V and 10W. The control signal input to the drive control circuit 10U is amplified by the amplifier 11 and is input to the light emitting diode LED of the photocoupler 12 through the protective resistance 13 so as to be output through its insulation, as the insulation signal, from the phototransistor PT. The insulation signal output from the collector C of the phototransistor PT, which is connected to the load resistance 14, is amplified by the drive circuit 15 and is input, as the drive voltage signal, to the gate G of the low-side IGBT 2U so as to perform on-off drive of the IGBT 2U. The drive control circuits 10V and 10W are also operated similarly so as to perform on-off drive of the IGBTs 2V and 2W, respectively. Likewise, the high-side IGBTs 1U, 1V and 1W are also subjected to on-off drive by corresponding drive control circuits (not shown) respectively such that a variable speed control of the three-phase induction motor 8 is performed by PWM control.
In addition, the background inverter shown in FIG. 11 is arranged and operated as described above. Negative poles of the output circuit sections of the drive control circuits 10U, 10V and 10W should essentially have an identical potential and may be operated by a single power source. However, variations of reference potentials of the IGBTs 2U, 2V and 2W may be caused by generating an induced voltage such as a surge voltage upon opening or closing of the IGBTs 2U, 2V and 2W due to the parasitic inductances Lu, Lv and Lw in the lines connecting the emitters E of the IGBTs 2U, 2V and 2W and the input terminal N, respectively, thereby resulting in malfunction or breakdown of the circuit.
To prevent the above malfunction of the circuit, it is necessary to provide level shift circuits in which levels of reference potentials of the drive voltage signals can be shifted from reference potentials of the PWM control circuit so as to follow up the reference potentials of the IGBTs 2U, 2V and 2W, respectively. In addition, the control signals (PWM signals) output from the PWM control circuit are converted into the drive voltage signals in a floating state so as to be input to the gates G of the IGBTs 2U, 2V and 2W. In the above mentioned background art, the photocoupler 12 is inserted, as the level shift circuit, into each of the drive control circuits 10U, 10V and 10W. Further, the DC drive power sources 17U, 17V and 17W are independently provided for the respective phases at the output circuit sections of the drive control circuits 10U, 10V and 10W.
The photocoupler 12 formed by the light emitting diode LED and the phototransistor PT is completely insulated between its input and its output and functions as the level shift circuit quite excellently. However, the photocoupler 12 has such drawbacks that its service life is limited and is not only larger in volume but more expensive than other semiconductor elements. Meanwhile, since the DC drive power sources 17U, 17V and 17W are required to be provided independently for the respective phases, such problems arise that the device becomes expensive and it is difficult to make the device compact.
Furthermore, an arrangement is known which includes a protective circuit (not shown) having a function of detecting an abnormality of a power source voltage, etc. supplied from outside to prevent a breakdown of the respective IGBTs of the above circuit. However, an arrangement does not exist which has a function of protecting deterioration of the IGBTs by self-diagnosis.
Meanwhile, to prevent breakdown of the respective IGBTs of the above circuit due to a surge voltage between the gate G and the emitter E of each IGBT, a self-protection circuit (not shown) is provided in which a pair of Zener diodes reversely connected to each other in series are inserted between the gate G and the emitter E. Namely, a surge voltage generated between a collector C and the emitter E is divided by parasitic capacities between the collector C and the gate G and between the gate G and the emitter E so as to be applied between the gate G and the emitter E. If this applied voltage exceeds a withstand voltage of the gate G, the respective IGBT breaks down. Thus, to protect each IGBT from the surge voltage, a pair of the Zener diodes reversely connected to each other in series are inserted between the gate G and the emitter E so as to restrict the voltage generated between the gate G and the emitter E to not more than a breakdown voltage of the Zener diodes. However, since a dynamic resistance of the Zener diodes is large, the Zener voltage becomes transitionally larger than its rated value at the time of generation of the surge voltage, so that it has been impossible to sufficiently restrain overvoltage caused by the surge voltage generated between the gate G and the emitter E.
Meanwhile, to obtain a signal insulated from an output line, a non-contact type current detecting element (not shown) such as a Hall element, a current transformer or the like is generally used in a background current detecting device (not shown) incorporated in the switching semiconductor element. However, in case the non-contact type current detecting element referred to above is used, such drawbacks are incurred that it is difficult to make the current detecting element compact and its detection accuracy is low due to the non-contact type.
Accordingly, one object of the present invention is to solve the above-noted and other problems.
Another object of the present invention is to provide a highly reliable power converter in which switching semiconductor elements forming a main circuit and their drive circuits are free from malfunction and breakdown.
To achieve these and other objects, the present invention provides in a first example a power converter including a main circuit having a plurality of semiconductor element rows, each having a plurality of semiconductor elements connected to one another in series. Also included is a DC main power source connected between junctions of the semiconductor element rows and a load connected to a series junction of the semiconductor elements in each of the semiconductor element rows.
Further, the semiconductor element rows are connected, at opposite ends of each of the semiconductor element rows, to one another in parallel and at least one of the semiconductor elements in each of the semiconductor element rows is a switching semiconductor element. Further provided is a level shift circuit to the switching semiconductor element and which receives a control signal at its input side and shifts, relative to a reference potential at the input side, a level of a reference potential at its output side so as to follow up variations of a reference potential of the switching semiconductor element. Also included is a drive circuit which receives a signal from the level shift circuit so as to output a drive signal to the switching semiconductor element, and a DC control power source for supplying electric power to the input side of the level shift circuit. In addition, electric power supplied from the DC main power source is converted into an alternating current or an on/off current in response to input of the control signal so as to be supplied to the load.
Further, the level shift circuit includes a transistor having a negative pole not only connected to a negative pole of the DC control power source but having the reference potential connected at the input side of the level shift circuit, a gate for receiving the control signal, and a positive pole for outputting, by shifting a level of a reference potential of the control signal input to the gate, the control signal to the drive circuit.
In addition, a point of the main circuit is connected to a negative pole of the DC main power source; and one of
(1) at least one of an inductor and a resistance, which is inserted between the point of the main circuit and the negative pole of the DC control power source;
(2) a capacitor which is inserted between the negative pole of the DC control power source and a reference potential point of the output side of the level shift circuit;
(3) at least one of a resistance and an inductor, which is inserted between a reference potential point of the output side of the level shift circuit and a negative main pole of the switching semiconductor element corresponding to the level shift circuit;
(4) at least one of an inductor and a resistance, which is inserted between the point of the main circuit and the negative pole of the DC control power source and a capacitor which is inserted between the negative pole of the DC control power source and a reference potential point of the output side of the level shift circuit;
(5) at least one of an inductor and a resistance, which is inserted between the point of the main circuit and the negative pole of the DC control power source and at least one of an additional resistance and an additional inductor, which is inserted between a reference potential point of the output side of the level shift circuit and a negative main pole of the switching semiconductor element corresponding to the level shift circuit;
(6) a capacitor which is inserted between the negative pole of the DC control power source and a reference potential point of the output side of the level shift circuit and at least one of a resistance and an inductor, which is inserted between a reference potential point of the output side of the level shift circuit and a negative main pole of the switching semiconductor element corresponding to the level shift circuit; and
(7) at least one of an inductor and a resistance, which is inserted between the point of the main circuit and the negative pole of the DC control power source, a capacitor which is inserted between the negative pole of the DC control power source and a reference potential point of the output side of the level shift circuit and at least one of an additional resistance and an additional inductor, which is inserted between a reference potential point of the output side of the level shift circuit and a negative main pole of the switching semiconductor element corresponding to the level shift circuit.
Since the transistor is used in the level shift circuit as described above, longer service life, more compactness and lower power consumption can be obtained in comparison with a background level shift circuit employing a photocoupler. In addition, since a surge voltage caused by a parasitic inductance of a line of the main circuit, especially a minus surge voltage leading to a higher potential at its negative pole through potential reversal is cancelled or restrained by inserting the inductor, the resistance or the capacitor into the level shift circuit and the drive circuit, and a breakdown of the transistor and malfunction of the switching semiconductor element can be prevented.
The present invention also provides in a second example a power converter including a main circuit having a plurality of semiconductor element rows each having a plurality of semiconductor elements connected to one another in series. Also included is a DC main power source connected between junctions of the semiconductor element rows and a load connected to a series junction of the semiconductor elements in each of the semiconductor element rows. Further, the semiconductor element rows are connected, at opposite ends of each of the semiconductor element rows, to one another in parallel and at least one of the semiconductor elements in each of the semiconductor element rows is a switching semiconductor element.
Also included is a level shift circuit which is provided correspondingly to the switching semiconductor element and which receives a control signal at its input side and shifts, relative to a reference potential at the input side, a level of a reference potential at its output side so as to follow up variations of a reference potential of the switching semiconductor element. Further included is a drive circuit which receives a signal from the level shift circuit so as to output a drive signal to the switching semiconductor element, and a DC control power source for supplying electric power to the input side of the level shift circuit.
Electric power supplied from the DC main power source is converted into an alternating current or an on/off current in response to an input of the control signal so as to be supplied to the load. In addition, a capacitor is inserted between positive and negative feeding points common with the drive circuit and the output side of the level shift circuit corresponding to a low-side switching semiconductor element of each of the semiconductor element rows, and a diode is inserted between a positive pole of the DC control power source and the positive feeding point such that a cathode of the diode is connected to the capacitor.
In addition, a point of the main circuit is connected to a negative pole of the DC main power source, and at least one of an inductor and a resistance, which is inserted between the point of the main circuit and a negative pole of the DC control power source.
Since a charging circuit formed by the diode and the capacitor is employed as a drive control power source for the output circuit section set in a floating state relative to the input circuit section in the level shift circuit and the drive circuit and electric power is supplied from the DC control power source as described above, effects of a surge voltage produced in a main power source line is less likely to be exerted even in the single power source in the same manner as a case in which an insulated DC drive power source is provided for each phase, thereby resulting in improved noise margin and more compactness.
In a third example, the present invention is directed to a power converter of the first example and includes an additional capacitor which is inserted between positive and negative feeding points common with the drive circuit and the output side of the level shift circuit, and a diode which is inserted between a positive pole of the DC control power source and the positive feeding point such that a cathode of the diode is connected to the capacitor. Further, a point of the main circuit is connected to a negative pole of the DC main power source. Also included is at least one of an inductor and a resistance, which is inserted between the point of the main circuit and the negative pole of the DC control power source.
Since the transistor having an insulated gate is used in the level shift circuit as described above, a longer service life, more compactness and lower power consumption can be obtained in comparison with a background level shift circuit employing a photocoupler. In addition, since a surge voltage caused by a parasitic inductance of a line of the main circuit, especially a minus surge voltage is cancelled or restrained by inserting the inductor, the resistance or the capacitor into the level shift circuit and the drive circuit, a breakdown of the transistor and malfunction of the switching semiconductor element can be prevented.
Furthermore, since a charging circuit formed by the diode and the capacitor is employed as a drive control power source for the output circuit section set in floating state relative to the input circuit section in the level shift circuit and the drive circuit and electric power is supplied from the DC control power source as described above, effects of a surge voltage produced in a main power source line is less likely to be exerted even in the single power source in the same manner as a case in which an insulated DC drive power source is provided for each phase, thereby resulting in improved noise margin and more compactness.
Meanwhile, in a fourth example the present invention is directed to a power converter of the second or third examples, and includes at least one of an additional inductor and an additional resistance, which is inserted between an anode of the diode and the positive pole of the DC control power source so as to form a series circuit with the diode. Also included is an additional capacitor which is inserted between the point of the main circuit and the anode of the diode.
Since a surge voltage produced in the main circuit is not only prevented from entering the input circuit section of the level shift circuit by at least one of the additional inductor and resistance and at least one of the inductor and the resistance, which is inserted between the point of the main circuit and the negative pole of the DC control power source, but is by-passed by the additional capacitor, the diode and the capacitor inserted between the drive circuit and the output side of the level shift circuit, a drive control circuit formed by the level shift circuit and the drive circuit is hardly affected by the surge voltage.
A fifth example of the present invention is directed to a power converter of one of the first to fourth examples (discussed above) in which the switching semiconductor element is an insulated gate type transistor. In this case, the power converter further includes a gate voltage detecting circuit which has a comparison voltage source for outputting a comparison voltage lower than a normal gate voltage of the transistor and higher than an abnormal gate voltage of the transistor, and a comparator for comparing a voltage of the insulated gate with the comparison voltage so as to output an abnormality signal in case the voltage of the insulated gate is lower than the comparison voltage.
Thus, it is possible to perform self-diagnosis on failure and deterioration of the transistor, the drive circuit, etc. Namely, a state in which the voltage of the insulated gate is lower than the comparison voltage when the drive signal has been output represents occurrence of troubles such as (1) a short circuit between the insulated gate and the negative main pole in the transistor, (2) a failure of the drive circuit and (3) a drop of an output voltage of the DC drive power source for supplying electric power to the drive circuit. Upon occurrence of one of these troubles, a disorder detection signal Fo is output such that abnormality of the transistor and the drive circuit can be easily detected highly reliably.
Furthermore, a sixth example of the present invention is directed to a power converter of the fifth example in which there is a time lag between a first time point of input of the control signal to the drive circuit and a second time point of output of a normal signal by the gate voltage detecting circuit. Further, the power converter includes an abnormality signal invalidating circuit which outputs, during a predetermined period from the first time point to a third time point occurring at or after the second time point, the normal signal by invalidating the abnormality signal output by the gate voltage detecting circuit.
Since the time lag for a rise of the gate voltage is produced by a parasitic capacity between the insulated gate and the negative main pole, the disorder detection signal Fo output by the gate voltage detecting circuit even when the transistor or the drive circuit is normal is invalidated such that high reliability free from erroneous automatic protection is obtained.
Meanwhile, a seventh example of the present invention is directed to a power converter of one of the first to sixth examples in which the switching semiconductor element is an insulated gate type transistor. In this example, the power converter further includes a capacitor which is inserted in parallel with the drive circuit of the transistor such that a negative pole of the capacitor is connected to a negative main pole of the transistor, a first diode which is inserted between a junction of a positive feeding point of the drive circuit and the capacitor and the insulated gate such that an anode of the first diode is connected to the insulated gate, and a second diode which is inserted between the insulated gate and the negative main pole such that a cathode of the second diode is connected to the insulated gate.
High reliability is obtained inexpensively such that it is possible to positively prevent a breakdown of the insulated gate and the drive circuit due to a surge voltage applied between a positive main pole and the negative main pole of the transistor, especially a minus surge voltage leading to higher potential at its negative pole through potential reversal.
An eighth example of the present invention is directed to a power converter of one of the first to sixth examples in which the switching semiconductor element is an insulated-gate transistor having a current detecting terminal provided in parallel with a negative main pole of the transistor. In this example, the power converter further includes a shunt resistance which is inserted between the current detecting terminal and the negative main pole of the transistor, a DC comparison voltage source which has a reference potential at the negative main pole of the transistor, and a comparator in which one of a pair of input terminals is connected to a junction of the shunt resistance and the current detecting terminal and the DC comparison voltage source is connected to the other of the input terminals. In addition, the comparator compares a potential difference of the shunt resistance with a voltage of the DC comparison voltage source so as to output an overcurrent detecting signal of the insulated-gate transistor. Also included is a capacitor which is inserted in parallel with the drive circuit of the insulated-gate transistor, between positive and negative feeding points of the drive circuit, with the negative feeding point being connected to the negative main pole of the transistor, a first diode which is inserted between the positive feeding point and the insulated gate such that an anode of the first diode is connected to the insulated gate, a second diode which is inserted between the insulated gate and the current detecting terminal such that a cathode of the second diode is connected to the insulated gate, and a third diode which is inserted between the current detecting terminal and the negative main pole of the transistor such that a cathode of the third diode is connected to an anode of the second diode.
High reliability is obtained inexpensively such that not only an overcurrent of the insulated-gate bipolar transistor having the current detecting terminal can be detected but it is possible to positively prevent a breakdown of the insulated gate, the drive circuit, the comparator for overcurrent detection, etc. due to a surge voltage applied between a positive main pole and the negative main pole of the transistor, especially a minus surge voltage leading to higher potential at its negative pole through potential reversal.
Meanwhile, a ninth example of the present invention is directed to a power converter of one of the first to eighth example and includes a shunt resistance which is inserted into an output line connecting the main circuit and the load, an amplifier for amplifying a voltage drop of the shunt resistance, a pulsing circuit which receives an output signal of the amplifier so as to output a pulse signal subjected to pulse width modulation, and an additional level shift circuit in which a reference potential at its input side is set in a floating state relative to that at its output side. The additional level shift circuit receives the pulse signal so as to transmit the pulse signal from the input side to the output side by shifting a level of a reference potential of the pulse signal such that a load current is detected on the basis of an output signal of the further level shift circuit.
Namely, the detection signal is transmitted by the level shift circuit to the output side set in a floating state relatively and the pulsing circuit for converting the analog detection signal into a digital signal optimized for minimization of the number of pulses per unit time, i.e., the pulse signal subjected to pulse width modulation is provided upstream of the level shift circuit. Accordingly, since the detection signal can be transmitted through the level shift circuit efficiently and a non-contact type current detecting element is not required to be used for detecting the load current, a compact and highly accurate detecting unit of low power consumption is obtained and can be incorporated into a package.